Pilots typically use landing navigation systems when they are landing an aircraft. These systems assist the pilot in maintaining the aircraft along a predetermined glide path associated with a particular landing strip or runway. In general, ground-based navigational systems are employed. Two common ground-based navigation systems currently in use are the Instrument Landing System (ILS) and the Microwave Landing System (MLS).
Due to limitations in the ILS and MLS Systems, including cost and single approach limitations, the Federal Aviation Administration (FAA) is transitioning the National Airspace System (NAS) from ground-based navigational systems to satellite-based navigational systems. In this endeavor, the FAA, with assistance from industry, is developing a Local Area Augmentation System (LAAS) to provide a satellite-based aircraft landing solution, which is designed to assist the pilot during approach and landing of an aircraft.
The LAAS uses a differential global positioning system (DGPS). The DGPS includes a global positioning system (GPS) and at least one ground station. The GPS uses a number of orbiting satellite stations and a receiver on an aircraft to determine the position of the aircraft with respect to the ground. With the satellite information, the receiver on the aircraft can determine the position, speed, and altitude of the aircraft. By adding a ground station, the DGPS can correct errors that may occur in the transmission of data from the satellites to the receiver on the aircraft. As a result, the DGPS may determine the position of the aircraft with a high degree of accuracy.
In 1998, the FAA initiated a program to develop requirements for developing and deploying a LAAS Ground Facility (LGF). The LGF will monitor the satellite constellation, provide the LAAS corrections and integrity data, and provide approach data to an interface with air traffic control. As a result of this program, the FAA released Specification, FAA-E-2937A, for a Category I LGF on Apr. 17, 2002, the contents of which are herein incorporated by reference. This specification establishes the performance requirements for the LGF.
The FAA specification requires the LGF to include a receiving antenna that meets specific requirements. With today's technology, a dual antenna may be required to meet the specific requirements. These two antennas are also referred to as the lower and upper antenna.